CPT® Code 45378

Last Updated: January 2026 | Verified for 2026 CMS & AMA Guidelines

Quick Reference: CPT 45378

• Definition: Diagnostic flexible colonoscopy (rectum to cecum) with NO therapeutic intervention (no biopsy, no polypectomy).
• Billing Rule: This is a "Base Code." Do not bill 45378 if a biopsy (45380) or polypectomy (45385) is performed; the therapeutic code supersedes it.
• Medicare Rule: Do not use 45378 for routine screenings for Medicare patients (Use G0105/G0121). Only use 45378 for diagnostic indications.
• Commercial Rule: Use 45378 with Modifier 33 for preventive screenings to ensure 100% coverage.
• 2026 Update: Medicare patients now owe 15% coinsurance if a screening turns therapeutic (polyp removal).

CPT 45378 is the foundational medical billing code for a diagnostic colonoscopy. This procedure involves an endoscopic examination of the entire colon (from rectum to cecum) using a flexible scope.

In this comprehensive 2026 guide, we explain the critical differences between screening and diagnostic exams, how to handle "converted" screenings (Modifier PT vs 33), and how to avoid NCCI bundling denials when performing biopsies and polypectomies in the same session.

1. Definition of CPT 45378

CPT 45378 is the base code for a complete flexible colonoscopy. The official AMA descriptor states:

"Colonoscopy, flexible; diagnostic, including collection of specimen(s) by brushing or washing, when performed (separate procedure)"

Included Services: The code inherently covers the diagnostic inspection of the colon up to the cecum (and potentially the terminal ileum). It also includes minor diagnostic maneuvers like:

• Collection of specimens by brushing or washing.
• Minor decompression of the colon (unless it qualifies as CPT 45393).

Exclusions: CPT 45378 is used only when the physician visualizes the colon but does not perform a biopsy, polypectomy, or other therapeutic maneuver. If a polyp is found and removed, the coding changes immediately to a therapeutic code (e.g., 45385).

2. Medical Necessity (ICD-10 Linking)

To ensure reimbursement, CPT 45378 must be linked to a valid ICD-10 diagnosis code supporting medical necessity. Indications generally fall into two categories:

Preventive Screening

Performed on asymptomatic patients to detect polyps or cancer early.

• Average Risk: Screening starts at age 45 (USPSTF guidelines).
• High Risk: Patients with family history or personal history of polyps.
• ICD-10 Codes: Z12.11 (Screening), Z80.0 (Family Hx), Z86.010 (Personal Hx of Polyps).

Diagnostic Evaluation

Performed when the patient has specific signs or symptoms.

• Gastrointestinal Bleeding: Code K92.2 (Unspecified hemorrhage) or R19.5 (Positive fecal occult blood).
• Iron-Deficiency Anemia: Code D50.0.
• Change in Bowel Habits: Code R19.4 or K59.1 (Diarrhea).

3. Comparison: CPT 45378 vs 45380 vs 45385

CPT 45378 is the "parent" code. If a therapeutic intervention occurs, you must select the code that represents the highest level of complexity performed. You generally cannot bill 45378 if you bill any of the codes below.

4. Screening vs. Diagnostic Rules

Billing for screening colonoscopy depends entirely on the payer. The workflow differs significantly between Medicare and Private/Commercial Insurance.

Medicare Coding Guidelines

• Routine Screening: Use HCPCS G0105 (High Risk) or G0121 (Average Risk). Do NOT use 45378 for screening.
• Screening Turned Therapeutic: If a polyp is removed during a G-code screening, you must switch to the CPT code (e.g., 45385) and append Modifier PT. This signals CMS to waive the deductible.
• 2026 Coinsurance Rule: For 2023-2026, if a Medicare screening turns therapeutic, the patient is responsible for 15% coinsurance (deductible is still waived).

flowchart TD
    A[Colonoscopy Encounter] --> B{Patient Type?}
    B -->|Medicare| C{Screening or Diagnostic?}
    B -->|Commercial| D{Screening or Diagnostic?}
    C -->|Screening| E[Use G0105 or G0121]
    C -->|Diagnostic| F[Use CPT 45378]
    E --> G{Polyp Found & Removed?}
    G -->|No| H[Bill G-code as-is]
    G -->|Yes| I[Switch to CPT 45385-PT]
    D -->|Screening| J[Use CPT 45378-33]
    D -->|Diagnostic| K[Use CPT 45378]
    J --> L{Polyp Found & Removed?}
    L -->|No| M[Bill 45378-33]
    L -->|Yes| N[Bill 45385-33]

Commercial Insurance Coding

• Routine Screening: Use CPT 45378. You must append Modifier 33 (Preventive Service) to ensure the patient has $0 cost-share under ACA rules.
• Screening Turned Therapeutic: If a polyp is removed, use the therapeutic CPT (e.g., 45385) with Modifier 33.

5. Advanced Modifier Guide (33, PT, 53, 52)

Using the wrong modifier can lead to claim rejections or improper patient billing.

• Modifier 33 (Preventive Service): Commercial Only. Indicates the primary intent was screening.
• Modifier PT (Colorectal Cancer Screening Test Converted to Diagnostic): Medicare Only. Used when a screening results in a procedure.
• Modifier 53 (Discontinued Procedure): Use when the colonoscopy cannot be completed to the cecum due to patient safety or poor prep. Medicare specifically prefers modifier 53 over 52 for discontinued screenings.
• Modifier 52 (Reduced Services): Used generally for reduced services at physician discretion, but less common for "failed" colonoscopy than modifier 53.
• Modifier 59 / XS (Distinct Procedural Service): Used to unbundle codes. For example, if you snare a polyp in the transverse colon (45385) and biopsy a separate lesion in the sigmoid colon (45380), use 45385, 45380-59.

6. Real-World Coding Scenarios

Scenario 1: Medicare Screening (Normal) A 66-year-old Medicare patient (average risk) undergoes a screening. The scope reaches the cecum. No polyps found. Code: G0121 (Diagnosis: Z12.11). Note: Do not use 45378.

Scenario 2: Commercial Screening with Polyp Removal A 50-year-old with Blue Cross undergoes a screening. A 5mm polyp is removed by snare. Code: 45385-33 (Diagnosis: Z12.11 primary, polyp code secondary). Modifier 33 ensures the preventive benefit is applied.

Scenario 3: Medicare Screening turned Therapeutic A Medicare patient undergoes screening (G0105). A polyp is removed by snare. Code: 45385-PT. We switch from the G-code to the CPT code but add PT to waive the deductible.

7. Bundling & Documentation (NCCI Edits)

Critical Bundling Rule: CPT 45378 is bundled into ALL therapeutic colonoscopy codes. Never bill 45378 and 45385 together for the same session. Additionally, Biopsy (45380) is bundled into Polypectomy (45385) if performed on the same lesion.

Documentation Checklist:

• Indication: Clearly state if the patient is asymptomatic (screening) or symptomatic (diagnostic).
• Extent: Document that the scope reached the cecum or terminal ileum.
• Site Specificity: "Polyp A (sigmoid) removed by snare; Polyp B (transverse) biopsied by cold forceps." Specificity allows for unbundling with modifiers.
• Anesthesia: If moderate sedation is provided by the endoscopist, bill 99152 separately. If deep sedation (Propofol) is used by an anesthesiologist, they bill 00812/00811.

8. Frequently Asked Questions (FAQ)

Can I bill 45378 with 45385?

No. 45378 is a diagnostic code. If a therapeutic procedure (45385) is performed, the diagnostic exam is included in the payment for the therapeutic procedure. Do not bill both.

What if the colonoscopy was incomplete?

If the provider cannot advance the scope to the cecum (e.g., due to poor prep), bill the intended code (45378 or G0121) with Modifier 53 (for physician) or Modifier 74 (for facility). Do not switch to a flexible sigmoidoscopy code (45330).

Does Medicare cover follow-up after a positive Cologuard?

Yes. As of 2023, a colonoscopy following a positive non-invasive stool test (like Cologuard or FIT) is considered part of the screening continuum. It should be billed as a screening (using modifiers if therapeutic) and cost-sharing is waived.